Video discs are encased in a permanent packaging comprising a molded spine which supports a 12 inch diameter (30.5 cm) video disc inside an outer plastic package or caddy. The caddy comprises two molded halves which are bonded together on three sides, leaving one side open for insertion and removal of the video disc during playback. The manufacture of the caddy requires molding of the two caddy halves, and ultrasonically welding or bonding the two caddy halves together. The video disc is placed on its spine and both are inserted into the caddy.
The dimensional tolerance of the parts are quite critical; if the caddy halves should bow inwardly, they may contact the video disc thereby damaging its surface; if the caddy halves should bow outwardly, the opening in the caddy into which the video disc must be inserted and removed will become too large (fishmouth) and difficulty may be encountered in inserting the caddy into the player thereby preventing proper operation during insertion and removal of the disc. The maximum tolerances for flatness of the caddy halves are .+-.0.02 inch (.+-.0.05 cm).
The manufacturing operations introduce various stresses into the plastic material of the caddy. When the caddies are stacked for shipment or storage for lengthy periods of time, these stresses tend to be relieved, particularly when stored at elevated temperatures. This results in a loss of dimensional integrity in the parts. If the caddy halves fall in on one another during this process, the video disc may be scratched or damaged by rubbing against the caddy during removal or insertion, or even prove impossible to readily remove from the caddy.
Thus a process which will stress-relieve the caddy parts and improve their long-range dimensional tolerances and stability was sought.